FIG. 1 shows an example of schematic view of a recording and reproducing head 11, a swing arm 12 and a disk medium 13 in a prior art magnetic disk apparatus. In case of recording and reproducing information onto a plane substrate in general, an access operation to select a position at which an information is recorded and reproduced is necessary. In addition, in order to record and reproduce the information while the track is being scanned consecutively, tracking operation for keeping the recording and reproducing head at the track is necessary. For these operations, it is necessary to position accurately the recording and reproducing head 11 with respect to the disk 13. Therefore, a prior art magnetic disk apparatus has a recording and reproducing head 11 mounted on the tip of a swing arm 12 so that the direction of the swing arm 12 is accurately controlled with a voice coil motor 14 disposed at the root of the swing arm 12. The recording and reproducing head 11 is a slider of a floating type, which is attached to the tip of the swing arm 12 through a suspension 15. The recording and reproducing head 11 is pressed against the disk 13 rotating rapidly with an appropriate weight by the suspension 15 so as to float stably at a predetermined height.
FIG. 2 is an enlarged view showing a bottom surrounding the recording and reproducing head 11. A friction face of an appropriate recess-projection structure is formed on the bottom of the recording and reproducing head 11 so as to give rise to good floating characteristics. In addition, to the rear end (from the friction direction) of the bottom of the recording and reproducing head, a magnetic flux detecting device 21 and a recording magnetic field generating device 22 are attached approximately parallel to each other and approximately perpendicular to the swing arm shaft 23. On the other hand, the disk medium 13 incorporated into the magnetic disk apparatus as a rotation member is provided with a number of tracks 16 at a constant pitch in a concentric circular state or a spiral state, and servo information, address information and recording data etc. are provided consecutively along these tracks.
In the prior art magnetic disk apparatus having the configuration as described above, the track is directed approximately perpendicular to the radius direction of a disk while the direction of the recording and reproducing head is determined by the direction of the swing arm shaft. Accordingly, it is impossible to always keep the magnetic flux detecting device 21 and the recording magnetic field generating device 22 parallel to the track orientation, and they are inclined by maximum 20° with respect to the track orientation. However, since the magnetic flux detecting device 21 and the recording magnetic field generating device 22 are fixed onto the same head, the relative direction between them is constant, and as shown in FIG. 3, a difference in shape between the magnetic domain 31 recorded by the recording magnetic field generating device and the magnetic flux detecting device 32 is small at any track position.
On the other hand, in recent years, studies on a system for recording by way of thermo-magnetic recording and reproducing by way of magnetic flux detection are being progressed. This technology is described in detail in JP-A-10-21598, for example. In this example, the recording light from a light source is irradiated through a transparent substrate to an optical magnetic recording film formed on a recording medium so that a magnetic domain is formed in the heated portion of the recording film and thus recording is executed. On the other hand, reproduction of information is executed by irradiating the reproducing light from the light source to the above described optical magnetic recording film through the substrate to detect rotation of the plane of polarization of the reflected light, and forming a second magnetic layer on the optical magnetic recording film to detect the leaked magnetic flux from this second magnetic layer.
Further, in 13-B-03 as well as 13-B-04 in Magneto Optical Recording International Symposium '99 Technical Digest, a system for executing recording by way of thermo-magnetic recording and executing reproducing by way of magnetic flux detection is disclosed further concretely. As the disk substrate, the polycarbonate substrate having the recess-projection structure on the surface is used while rare-earth transition metal alloy with TbFeCo as main material is used for the magnetic recording film. Since the recess-projection structure of the substrate surface can be used as servo information of light spots, the same servo information can be used for both of the optical recording system and the magnetic flux reproducing system so that the recess-projection structure is particularly suitable for this system. In addition, for a recording system, one of thermo-magnetic recording methods called as optical pulse magnetic field modulation method is used. Since the optical pulse magnetic field modulation recording system can keep the recording power margin wide in case of that a magnetic domains shorter than the diameter of the light spot (approximately 1.0 micron) in the track scanning direction are recorded, the optical pulse magnetic field modulation recording system is advantageous. In the above described known example, it is described that recording of 0.1 micron length equivalent to about one-tenth of the light spot diameter (approximately 1.0 micron) focused to the diffraction limit is obtainable.
However, since the magnetization direction in the approximately circular region is determined at every optical pulse irradiation in the above described optical pulse magnetic field modulation recording, the recording magnetic domain becomes approximately crescent. Therefore, in the case where reproduction is executed with normal magnetic flux detecting means with sensitivity distribution being approximately linearly shaped, the recorded magnetic domain is different in shape from the magnetic flux detecting means, therefore giving rise to a problem of deterioration in reproducing performance. That is, since the time where the magnetic flux detecting means passes the magnetic wall varies in accordance with the distance from the center of the track so that the response waveform from the recording magnetic domain expands in the time direction in coordinates, MTF of the reproducing system will be deteriorated, giving rise to increase in jitter of signal or worse resulting in increase in error rates or decrease in reliability. In addition, the magnetic walls approach extremely close to each other at the tip of the approximately crescent-shaped recording magnetic domains, giving rise to unstability easily followed by unexpected magnetic domain shape. The response from this portion is different from the originally recorded user data, and therefore will become a noise, preventing normal reproduction of user data. As a result described above, it was difficult to improve the recording density.
In order to cope with such a problem, a method using an optical head for elongating radially the shape of the light spot is considered. For example, the “Optical information recording apparatus” in Japanese Patent No. 2858455 specification describes a method in which a phase shift device having a partition line in a direction transversing the information track is disposed in the optical path of the optical head and the beams from the optical head are irradiated as two optical recording spots juxtaposed in the direction transversing the information track so that the heat distribution is effectively elongated perpendicular to the track and curvature of the recorded magnetic domain is made small. For similar effect, means (phase mask and intensity mask etc.) for adjusting appropriately the shape of the irradiated light spot may be arranged on the optical path of the optical head. Otherwise, for example, by a cylindrical lens arranged in an optical system to adjust a focusing position, an approximately oval-shaped optical spot can be formed on the recording film surface so that the short-side axis direction of the oval light spot is parallel to the track.
With such a prior art, also in the thermo-magnetic recording system, the recording magnetic domain having the magnetic wall transversing the track orientation can be formed. However, in the thermo-magnetic recording system as the above described prior art, the orientation of the recorded magnetic domain is constant from the inner circumference to the outer circumference of the disk. On the other hand, on accessing or tracking the magnetic domain formed in this system with the recording and reproducing head attached to the tip of the swing arm as in the prior art magnetic disk apparatus, the magnetic flux detecting means is directed variously according to the respective track position as described above. Therefore, in the innermost circumference and the outermost circumference of the tracks in particular as shown in FIG. 4, the direction of the magnetic wall of the recorded magnetic domain and the direction of the magnetic flux detecting means will be no longer in accord with each other. Accordingly, in case of combining the prior art magnetic flux detecting system for the magnetic disk with the prior art thermo-magnetic recording system, it is difficult to reproduce the recorded magnetic domain in high signal quality over all of the tracks from the inner circumference to the outer circumference.
An object of the present invention is, in view of the conventional construction of the magnetic disk apparatus as described above, to provide an information recording/reproducing apparatus and an information recording medium, in which a magnetic domain recorded by a thermo-magnetic recording system can be reproduced in the equivalent high signal quality over the whole disk area by a reproduction system with a magnetic flux detecting means mounted on a forward end of a swing arm.